The present invention relates to a power supply circuit and, more particularly, to a reset pulse generator for developing an initial reset pulse to be applied to a logic circuit such as a microcomputer.
Recently, many kinds of electric apparatus such as a microwave oven employ a microcomputer for controlling an operational mode of the electric apparatus. In such a microcomputer controlled system, the registers included in the microcomputer must be cleared when the power supply switch is switched on. That is, the memory state must be first cleared and, then, a desired program must be conducted. Therefore, an auto clear system is provided to develop an initial reset signal when the power supply switch is switched on.
However, the conventional auto clear system can not ensure a stable operation of the microcomputer. Especially, when a momentary interruption of the electric service occurs, there is a possibility that the initial reset signal is not developed when the electric service is immediately recovered even though the contents of the microcomputer must be cleared to ensure a stable operation.
Accordingly, an object of the present invention is to provide a novel reset pulse generation circuit for developing an initial reset pulse to be applied to a microcomputer included in an electric apparatus such as a microwave oven.
Another object of the present invention is to provide a reset pulse generation circuit included in a power supply circuit, which develops an initial reset pulse even when the electric service is recovered after a momentary interruption of the electric service.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a reset pulse generation circuit is included in a power supply circuit having a regulator circuit. The reset pulse generation circuit includes a series circuit of a Zener diode and a resistor. The thus formed series circuit is connected to a smoothing capacitor included in the regulator circuit in a parallel fashion. The node provided between the Zener diode and the resistor develops an initial reset pulse to be applied to a microcomputer included in an electric apparatus such as a microwave oven.